If you didn't know your Bible, in fact, you could be forgiven for wondering what God will do with a man like Abram, who disobeyed God in taking Lot and all the goods of his father's house off to Canaan, and who then abandoned the land of promise for Egypt, where he also lied about and then gave up the wife needed for the child of promise in exchange for a good dowry from Pharaoh. In short, Abraham has sinned and rejected all the things God had promised to go his own way. Yet in chapter 15 God is right there, re-affirming His covenant with Abraham.
And He does so in a most unusual manner, instructing Abram to cut in half a heifer, a ram, and a goat, and to lay out a young pigeon and a dove, leaving a bloody aisle between the halves. This was part of a covenant making and/or sealing ceremony, in which the covenant participants walked the aisle between the pieces, and in so doing laid on themselves an implied death sentence if they break the covenant (i.e., "May it be done to me like these animals"). But after all is arranged, it is God alone (symbolized by the torch and smoking firepot, v. 17), who passes through, symbolizing that it is God alone who will keep the covenant, since He alone made it.
In this, I find great personal encouragement and even sanctifying grace. For, as Paul says in Romans 15:4, "Everything that was written in the past was written to teach us..." And what this little incident reminds me is that I have a much better covenant than Abram, for mine was sealed not with God symbolically pronouncing death on Himself, but with the actual slaughter of the Son of God, whose death paid for my covenant breaking and established a new one, which likewise God alone keeps with me. Through that covenant, enacted by God's merciful, holy love, I cannot be rejected despite my ongoing sinfulness, because God has already paid the penalty for my sin. And since no matter what I've done or do, God is right there re-affirming His love for me, I am motivated each day to confess my sin and live in greater obedience. This is indeed, amazing grace.